American Chemists detail ways to improve ethanol yields from grains.

[NNadir]

This is an offshoot of the much ballyhooed "cellulosic ethanol" discussions that one hears all the time.

There is considerable interest in using ethanol as an additive to gasoline and, ultimately, as a liquid fuel. Approximately 4 billion gallons of ethanol was produced in 2005, mostly from corn grain, an increase of 17% over the previous year and over twice as much as was produced in 2001.1 The Energy Policy Act, signed into law in August 2005, requires that 7.5 billion gal/year of biofuels, most notably ethanol, are to be mixed with gasoline by 2012.2 Several states in the Midwest have adopted or are considering more stringent renewable fuel standards. To meet this need, 29 new ethanol plants are under construction to add to the 95 plants operating as of January 2006.1 Thus, demand for ethanol in the United States is expected to continue its rapid growth in the near future. The dominant process for producing grain ethanol in the United States is the dry-grind process, which contributes about 79% of current ethanol production. During this process, distiller’s dry grain and solubles (DDGS) is created as a coproduct, and over 9 million metric tons of this material was produced in 2005.3 This residue has a high protein content and is currently used primarily as feed for the beef and dairy industry, while it is used only sparingly in the poultry and swine feed markets. However, as the supply of DDGS increases, its price is expected to decrease in relation to other feeds such as soybean meal.

Thus, it may be necessary to increase the value of DDGS in order to keep dry-grind ethanol plants cost competitive. One possible approach is the enzymatic hydrolysis of the cellulose into glucose for fermentation into ethanol. The remaining grain would have a higher protein content, thereby increasing its value and possibly allowing it to expand more fully into the swine and poultry markets. The increase in ethanol production due to cellulose hydrolysis would also provide additional economic benefit. Tucker et al. reported ethanol yields of 73% of the theoretical value using dilute-acid pretreatment and also demonstrated that the resulting hydrolyzed distiller’s grain could be included in turkey feed at up to 10% total feed.4

Cellulose is resistant to enzymatic hydrolysis due to its densely packed and rigid crystalline structure. A novel pretreatment method to improve the efficiency of enzymatic hydrolysis
is the ammonia fiber expansion (AFEX) process. Liquid ammonia binds to the cellulose under high pressure (200-500 psi) and moderate temperatures (70-100 °C). The pressure is then quickly released. Virtually all of the ammonia can be recovered. This process decrystallizes the cellulose, hydrolyzes hemicellulose, removes and depolymerizes lignin, and increases the surface area available for hydrolysis, thereby significantly increasing the rate of enzymatic hydrolysis...

This is from Energy & Fuels 2006, 20, 2732-2736.

This work produced increase glucose yields up to 108%, making it available for the production of more ethanol.